Abstract: Fluid flow ability in tight oil reservoirs is poor, and two media with obvious difference in matrix and fracture are formed after horizontal well fracturing.The seepage mechanism of fluid in two media is different, and there is a high start-up pressure gradient in the matrix.Coupling of different seepage laws brings new difficulties to the study of productivity and production performance of fractured horizontal wells in tight oil reservoirs.This paper establishes a productivity model of fractured horizontal wells in tight oil reservoirs considering the low-speed non-linear seepage law of different matrices, and studies the influence of start-up pressure gradient on the development performance of fractured horizontal wells in tight oil reservoirs.The whole production cycle is divided into four stages:first linear flow, fracture interference flow, second linear flow and boundary control flow.It is recognized that start-up pressure gradient can shorten the stable production stage of first linear flow and second linear flow, which is not conducive to the effective development of tight oil reservoirs.At the same time, the start-up pressure gradient has an important impact on the optimization of fracture parameters.The higher the start-up pressure gradient, the longer, denser and more cracks are needed to develop effectively.